Cable clamp



June 29, 1948. CLAYTON V 2,444,092"

CABLE CLAM? Filed Oct. 9, 1945 INVENTOR Martin M Clayton Patented June 29, 1948' I UNITED CABLECLA'MP =iviartin= Mi :Glayton; Enon Valley, Ra., -assignorl;to

National f Electric-Products .Qorpnratiog -Bittsburgh, Pa; a corpcrationmfirllelaware representatively in Patent No. 1,322.12??- to Martin vMxvelayt-on. and; No? Y 1 9-1 4", 635 to -William *Goetze'lman. The'first of the said*patents*dis- JCIDSES} azfitwo piece lcable clamp. and thelatten. a none-apiece :clamp. aWhereas there is advantagerin EADHQelJiECGECIdIHDi in'facilitatingl initial assembly handr'manipulationl while engaging :cables to Jan welltletf box, there is; a :serious-problem-involvediin "en agingnone-metallic :sh'eatlr ;cables, 7 or. xiloom wire by means of clamps oflthatsort. Armored eablewis readilyengagedv lay-cable clarnpsqtmwitm standa ,severerand -relatively, prolonged, pull; by ;-e1a-rnping ,downyon1 the cable-to engage it -.between rconvolutionseon. a verticaled e .of the ouh '-1et boxwall at a cable-receiving:opening ,therein. Engagernent oi; tha tSOltis not permissible in the ,icaseJ ofanon-metallic: sheath-.cab-le, because a severepull exerted ona cable of that sortrwhen clarhpedin that mannen tends to striplthe cover from the cable. Itcannotmbeconsidered either. a desirable or a secure jengagementw oir the cable, v ihasniuleh as ,ithconsists placing the sheath. of Ilthe ahleundena'shearing compression.

lThefobject rof. rnyinvention is to .provide a one- .piece'eable clamp} which, while particularly satisffalctory for thefclamping engagement ofr armored cable, exerts a'clarnping action of such sortthat *it" holds non' metallic sheathc'able securely with .aniengagement which tends torbecorneincreasin'glyfirmundr severe pull on the cable, by ,an

*fr'ee-*-ca ble-engaging edges presented angularly -"'against withdrawal of cables which have been increasing?"'tenc lenoyv penetratively to. gripjvthe clamped, which edges are disposedin assembly r close to t'heinterior surface of the outlet boxwall "through which the cables passyso "that "thereis a tendency I toebunch va ,ai-nst them the sheaths on ithe short lengths of non-metallic sheath cahleswhich extend into :the outletl-box. The .i

--clam-pingnaction is by means 'of flexion' exerted inward.- of: the saidifreeredges by means whichare not directly connected with them, and..-:which -leavethose edges free forltheir,.-penetrativefienzgagement ofithezcable sheath. l

rr-y-Inithe accompanying drawings; illustrative "of: a sphysical embiidimentnofl my invention:

'R E'ig 1 is acplaniviewnf mycable clamp mounted -between a yerticalswallfiofr nan aoutletibox. and the y r y r a a2 sheathcables engaged to the=outletlrboxeby the iclamp. r l 'FigrlI is a-perspectiveviewof the'cable clampunrelated to-other structure.

:rFigi III ist -a r view taken in :vertical section "through the twoua'cljacent wallslof-an outlet box: "at which the timer: is: mounted, iliustrating the engagement of armored cable-lay the iclamp.

ig: IV is asimilarwi'ew; illustrating the .en--' 1 "gagement of non metallicsheath cable -by the elainp.

'Figl-V is a perspective viewmf the-clamp with -one non -meta1llic ssheath --ca3ble engaged i thereby,v illustrating theefiect when a severe' withdrawing" pull is exerted on one of the-deiblesengaged =by th'e clamp. r

Fig 'VI is adongitudinahsectional :viewzthrough i'the r c'able illustrating J-the same efiect ishown i in "Figl-V, andataken irr :the plane of the sectionuline The cable cla-mp. of my "invention :is-u an onepiece structure 'composed of: yielding metal. 'J-It =comprises'a clamping bar- I; having an-upstan-rb ingfiskirtf 2:which in all conditions of the-clamp closes the cable -receivi-ngopenings 4 in arvertical tended backwardly from perforate :wall Gthere is a foot' La'daptedto rest on the bottom wall, or floor il *ofian outlet hoxuand perforate'at 9 for themassage "of a clampingscrew l0 threaded in the -floorJof-the box. f In' vertically spaced rela- \tion with" fcot Tthereds a pressure plate ll; ex-

tended inwardly from-clamping bar I1 and having P therein. a screw-receiving perforation; l 2 in alignmentwith th'eaperforaticn 9 ot-foot 1.

it lnirmounteduposition of. theiclamp, the skirt 2 uof the? clamping tibar liesi in surface rcontact; with, or rclosely; .lparallel'; to the interior surface (of. the aoutletzxboxwwall; and perforate wall 6 stands'at aylowerwlevel hutaapproximately parallel to, skin: ,2, wl-ith=;clamping.=scnew1:!0 :passed freely through :the ,=';m-atching perforations in pressure plate: I l "aandginrfoot Land engaging: its threaded opening y'intheflfloonofgtherboxl {There is of necessity con tnetctien ,hetweenirthe ;structure a of the rj=c am i e than and thez'structure -of-the bushedwalland its associated; foot;.and itis in: the, form and arrange- -mBnt'j-i 0f thermeansyfor making such zconnection .and'thexformeand arrangementeofithe clamping bargxitself :thatrthe; novel clamping :effect of my eazblerclampzrises.

bottom wall thereof, showing twoanom-metallic #1 i1ilhetzconneetlngEsmeansrare; 8/; pair -iofafiexible straps which spring from the upper edge of hushed wall 6 and. which extend to points of indirect connection with clamping bar 1 at such points as to leave free edges of the clamping bar on both sides of plate ll. These points of connection are with the sides of-plate H, and from such points the straps extend laterally and then inwardlytdwall 6, to leave intervals between them and the inwardly presented cable-engaging edges l of the clamping bar. Clamping bar I has a relatively short inward extent from the backing provided by its skirt 2, and is therefore relatively rigid. Its rigidity is increased and its clamping effect enhanced by-longitudinal corruations which provide indentations or downward extensions It, terminating at the clamping edges 15 longitudinally in line with the bushed openings in wall 6.

Under the pressure of screw ill on pressure plate ll, there is a force bearing downwardly on the outer structural elements of the clamp comprising the pressure plate II, the clamping bar l and its vertical skirt 2. Under this applied force straps l3 flex. Such flexion occurs chiefly at the junction between the lateral extent and the longitudinal extent of each strap, and involves a slight twisting as well as a downward bending of the straps. As the clamping bar moves downwardly with this flexion of the straps, its skirt 2 thus maintains its parallel relation and full surface contact with the wall of the outlet box, to give firm backing to the clamping bar. The chief clampin engagement with the cable is at the free inwardly presented edges I5 of the clamping bar.

Referring to Fig. III of the drawings which show armored cables A engaged to an outlet box by the clamp, it will be seen that theclamping edges 15, one. of which is visible, engages behind one of the convolutions a of the cable armor when screw I0 is run down. This gives an engagement of the cable by the clamp itself which is in direct opposition to forces tending to pull the cable from the outlet box as well as pressure exerted by the clamp normal to the axis of the cable. In clamping armored cable by means of my clamp, it is therefore unnecessary to place the openings 4 in the vertical wall of the outlet box so as to leave cable-engaging stub walls at the base of such openings, as in Clayton Patent No. 1,822,128 and Goetzelman Patent No. 1,914,635 referred to above. Such stub wall may therefore be omitted, if it is desired to avoid radial pinching of non-metallic sheath cable in outlet boxes intended, as is customary in the art, jfD! use with cables of both types.

Non-metallic sheath cable, or loom-wire has 'none of the properties which simplify the clamping of armored cable in an outlet box. That is, it does not present the hard, convoluted structure of the armored cable to provide firm irregularity for gripping engagement. On the contrary the surface of such cables is smooth and their structure is compressible; consisting as they do of rubber insulation, crumpled paper, braid, and one or more coatings of saturant, pitch, wax and the like surrounding the pair of electrical conductors they enclose. It has been explained above that the engagement of cables of that sort has been imperfect, even. though the clamping effect of compression alone be supplemented by cable-indenting deformation of the cable structure, or by a stub wall at the base of the outlet box openings against which the cable is pressed. In both cases a severe outward pull produces a scraping or furrowing effect on the jacket of the cable, so that the engagement yields under the exertion of a pull which is relatively moderate in applied force and duration. Clamps intended for the engagement of cables of both types in an outlet box, may therefore be effective for engaging armored cable but are relatively ineffective for engaging non-metallic sheath cable.

Referring to Fig. IV of the drawings, a nonmetallic sheath cable, or cables, B are shown enaged in an outlet box by my clamp, one such cable being visible. In this view it is seen that as the clamping screw I0 is run down, the structure of the cable is compressed between the clamp and the floor 8 of the outlet box, the compression being in large measure concentrated in those areas in which the downward indentations H; of the clamping bar are located. This causes the structure of the cable sheaths to bunch out inwardly of the clamping bar and upwardly beyond the free edges [-5 at the inward ends of the lndentations. This forms in the cable sheath a shoulder b inwardly of the cooperative edge l5 of the clamping bar and against which that edge bears.

In this clamped condition of the cable, a severe outward pull on the cable causes the cable-engaging edge It to bite in the bunched shoulder b, and as the pulling continues causes the cable sheath to be increasingly bunched at that edge. There is, even under the pressure against it, some tendency for th edge I5 to be slightly depressed, or tilted, and thus to bite more deeply into the cable sheath.

The above efiect, which is illustrated in Figs. V and VI of the drawings, results in an increasing security of clamping engagement under forces tending to pull the cable outwardly from engagement in the outlet box. My cable clamp thus takes advantage in a novel manner of those very properties of non-metallic sheath cable which previously have detracted from the security of its clamped engagement, to prow'de an engagement of superior and approved sort.

It will be noted that Fig. IV of the drawings does not show a stub wall against which the cable is forced by the clamp, the openings 4 in outlet box wall 5 having their lower peripheries touching the bottom wall, or floor, 8 of the box. This illustrates the fact that in use of my clamp such stub wall is unnecessary in clamping non-metallic sheath cable, as well as in clamping armored cable. It is a fact, however, that such stub wall may be present without detrimental efiect, because the firm engagement of the cable sheath against a free edge l5 of the clamping bar prevents positively withdrawal of the cableby scraping or furrowing against the edge of such wall.

It will be appreciated that the advantages of my cable clamp as explained above are all obtained without in any degree impairing the general advantages of a one-piece cable clamp, in facilitating initial assembly of the clamp with an outlet box and facilitating the clamping engagement of cables with the structure of the outlet box.

Having shown and described one specific embodiment of my invention, it is to be understood that such showing and description are illustrative and exemplary of that invention, and that changes in form and arrangement may be made within the boundaries defined by the claims appended hereto.

I claim as my invention:

1. A one-piece cable clamp for securing cables to an outlet box comprising a clamping-bar, a pressure plate extended from said clamping-bar, a wall member perforate for the passage of cables spaced from said clamping-bar, means for applying deflecting force on said pressure plate, said means being suificiently remote from the rear edge of said clamping bar to tilt said clamping bar when pressure is applied to the pressure plate, and yielding connector straps extended laterally from said pressure plate and longitudinally to said perforate wall providing free cable-clamping edges on said clamping bar and having points of fiexion adjacent the said cableclamping edges to force the cable-clamping edges of the clamping-bar into clamping engagement with cables lying beneath the clamping bar.

2. A one-piece cable clamp for securing cables to an outlet box comprising a wall member perforate for the passage of cables, a horizontally disposed clamping-bar spaced from the said wall and having depressed regions with cable-clamping edges presented toward the said wall member, a pressure plate extended from the said clamping-bar toward the said wall member, means for exerting a depressing force on said pressure plate, said means being sufficiently remote from the rear edge of said clamping bar to tilt said clamping bar when pressure is applied to the pressure plate, and yielding connector straps extended from said pressure plate to said wall member free of the cable-clamping edge of the said clamping-bar and arranged to flex under the application of depressing force on said pressure plate to bring the free cable-clamping edges of the clamping-bar into clamping engagement withcables lying beneath the clamping-bar.

3. A one-piece cable clamp composed of an in ward structure adapted to be anchored in an out: let box, an outwardstructure adapted to bear against the inner wall surface of the outlet box comprising aclamping-bar having free cableclamping edges presented toward the said inner anchored structure, yielding connector structure extended between said outward structure and said inward anchored structure adapted to flex under depressing forces to bring the free edges of the said clamping-bar into clamping engagement with cables which are to be secured to the outlet box, and means for applying depressing force on said connector structure, said means being sufiiciently remote from the rear edge of said clamping bar to tilt said clamping bar when pressure is applied to the connector structure.

MARTIN M. CLAYTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,711,912 Vaughn et al May 7, 1929 1,822,128 Clayton Sept. 8, 1931 1,914,635 Goetzelman June 20, 1933 Certificate of Correction Patent No. 2,444,092. June 29, 1948.

, MARTIN M. CLAYTON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 4, claim 1, and line 25, claim 2, for the word extended read extending forwardly; and that the said Letters Patent should be read with these corrections therein that the same may conform with the record of the ease in the Patent Office.

Signed and sealed this 12th day of'October, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommissz'oner of Patents. 

